NANOWRITING ON AN ATOMICALLY FLAT GOLD SURFACE WITH SCANNING TUNNELING MICROSCOPE

We present new experimental results of writing stable features on atomically flat surfaces of gold films. By applying successive voltage pulses across the tunneling gap in controlled atmosphere, nearly 150 individual holes are produced to record one message. The writing process has a higher success rate in nitrogen gas with the presence of water or ethanol vapour. Written letters remain stable for more than 4 days in dry nitrogen gas, in contrast to some previous STM results of monatomic step movement on the gold surface. By changing the vapour pressure, pulse amplitude and polarity, we succeed in controlling the gold surface modification (feature dimensions, choice of mound or pit). The smallest stable nano-hole formed is 3 nn in diameter and 0.24 mn in depth, which represents the loss of about 100 Au atoms. The destiny of these missing atoms is unknown but the clear-cut feature of the hole indicates that they have been moved far away. We report for the first time the existence of a minimum relative humidity (18% at 22 degrees C) for the formation of nano-hole, which implies that the reaction may be electrochemical in origin.